The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of the lens onto the retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens.
When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial lens.
In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, a thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by the artificial lens.
Prior to the introduction of the artificial intraocular lens into the eye, softer cortical material is aspirated from the eye using an aspiration tip. Aspiration tips are similar to phacoemulsification tips, but with a smaller opening at the distal end and not typically vibrated ultrasonically. The aspiration tip may also be used to “polish” the posterior capsule to remove residual epithelial cells and reduce the risk of posterior capsule opacification. Conventional aspiration tips are made from titanium or stainless steel. These tips must be highly polished to reduce burrs and eliminate sharp edges that may snag or tear the posterior capsule. Polishing the aspiration port and the interior lumen of the aspiration tip, however, is very difficult and some burrs may remain even after extensive polishing. During capsule polishing and cortical clean-up, the posterior capsule may be drawn partially into the aspiration port and interior lumen of the aspiration tip. If these portions of the aspiration tip contain rough edges or burrs, tearing of the posterior capsule can occur. In addition, during repeated use, the exterior of the aspiration tip can develop burrs and rough spots that can snag or tear the capsule.
One prior aspiration tip, disclosed in U.S. Pat. No. 5,718,677 (Capetan, et al.) overcomes the problems associated with metal tips by installing a silicone rubber tip cap over the distal end of the metal cannula. While the device is effective is reducing or eliminating some of the risks discussed above, the rubber tip cap must be fixed to the metal tip to prevent the tip cap from sliding off of the metal tip. While the rubber tip cap is sterilizable in an autoclave, the tip cap is much more easily damaged than the metal cannula, thereby limiting the number of reuses of the tip assembly. In addition, as with other commercially available tips, the tip cap does not provide any irrigation function, so a separate irrigation handpiece or an infusion sleeve over the aspiration tip must be used.
Accordingly, a need continues to exist for an irrigation/aspiration tip that reduces the possibility of tearing the posterior capsule during cortical clean-up and capsule polishing.